Lead-in seal structure



May 28, 1946. L N AL r 2,400,946

LEAD IN SEAL STRUCTURE Filed March 50, 1944 Fig.1.

Fig 2.

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Jack Whi't'temove,

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Patented May 28, 1946 LEAD-IN SEAL STRUCTURE Evan H. Nelson, Harrow Weald, and Jack Whittemore, Wembley, England, assignors to General Electric Company, a corporation of New York Application March 30, 1944, Serial No. 528,659 In Great Britain November 18, 1942 2 Claims.

This invention relates to methods of sealing electric conductors through vitreous (especially quartz) walls of the type wherein the conductor, where it makes molecular contact with the vitreous material, consists of a plurality of thin strips lying between a vitreous core (often hollow) and a vitreous jacket collapsed onto the strips and the core.

Seals of this kind are usually made separately from the envelopes of which they eventually form part, and after manufacture are sealed into apertures in those envelopes. If, as is usual, the conductor is designed to carr twenty or more amperes, the seal is necessarily bulky and the aperture in the envelope into which it is sealed may have to be undesirably wide. The necessary width of the aperture can be decreased'by joining the strips where they emerge from the inner end of the seal to a solid rod which, though its diameter is less than that of the core, may have a cross section Whose area is as great as the sum of the areas of the cross sections of the strips, and by continuing the said Jacket as a narrow tube surrounding the rod. The aperture need then be only as wide as the narrower tube. But then it is not immediately obvious how to make a junction between the strips and the rod that is satisfactory both electrically and mechanically. An

object of the invention is to solve this problem. Other objects and advantages of our invention will appear from the following description of a species thereof and from the drawing, wherein:

Fig. 1 is an elevation of a rod-like member forming part of a lead-in conductor; Fig. 2 is a plan view of another portion of the conductor: and Fig. 3 is an elevation, in section, of a completed seal structure.

According to the invention in a method of sealing an electric conductor through a vitreouswall, of the type specified, the said conductor preferably comprises the following parts, originally separate: (1) A rod reduced at one end to a pin of smaller diameter so that a shoulder is formed between the rod and the pin; (2) a cross piece having a plurality 11 (e. g. 4) of arms and a hole at its center through which the said pin i adapted to protrude; (3) a plurality n of strips each adapted to be welded to one of the said arms; and the said parts are assembled by welding the .said strips each to a said arm and uniting the cross piece to the rod by the use of the said pin as a rivet. The riveting may be performed either before or after the welding.

Referring to the drawing, in a specific embodiment the tungsten rod I is '70 mm. long and 4 mm.

in diameter. The pin 2 at one end is 1.5 mm. long and 1 mm. in diameter. The cross piece 3 is of molybdenum sheet' 0.1 mm. thick, and has the form of a square with 10 mm. sides, with arm pieces 4, each 9 mm. long and 10 mm. wide, prolonging its sides. A hole 5 just over 1 mm. in diameter pierces the center of the square. The molybdenum strips 6 are each mm. long, 9 mm. wide and 0.05 mm. thick. At the end remote from the cross piece, tags -'l are welded to the strips to serve as external leads, but these are not characteristic of the invention.

The pin 2 is pushed through the hole 5 so that the cross piece 3 rests on the shoulder between the pin 2 and the rod I. The upper part Of the rod and the pin are heated in a flame and, when the pin is at a full red heat, it is hammered down so that it acts as a rivet uniting the cross piece to the rod. The film of oxide resulting from this operation is removed by etching; the four strips 6 previously cleaned by etching are then welded to the four arms 4, as indicated in Figure 2; the strips overlap the arms over a length of some 3 mm. and the Welding is effected over substantially the whole area over which the strips and the arms contact.

Preferably thin strips of molybdenum (say 0.015 mm. thick) are welded to the cross piece 3 and the rod l where the quartz is to be collapsed onto these parts in the next stage. The intervention of such thin strips tends to prevent cracking in known manner, but is not always essential. These thin strips are omitted from the drawing for clarity.

The arms 4 with the strips 6 attached to them are now bent upwards from the plane of Figure 2 so that they lie roughly in the line of the rod. The hollow quartz core 8, closed at its inner end, is now placed between the strips and rests on the cross piece. The core is 18 mm. in external diameter and has walls 4 mm. thick. The assembly of conductor and core is then placed within a quartz tubular Jacket with walls some 2 mm. thick, having a wider upper part 9, some 19 mm.

-' in internal diameter, surrounding the strips and a narrow part. In, some 4.5 mm. in internal diameter, surrounding the rod. The lower end It is closed in order that the jacket may be evacuated during collapse in the usual manner. The jacket is now heated so that it collapses onto the core 8 over substantially all its-length and onto the rod over the upper portion thereof. When the seal cools there is molecular contact between the jacket, the core, and the strips, but the quartz shrinks away from the thicker cross piece 3 and rod I. The lower closed end 01' the jacket is now cut away; an electrode is attached to the free end or the rod; and the narrow part of the jacket is sealed into an aperture in an envelope, as indicated roughly at l2.

What we claim as new and desire to secure by Letters Patent 01 the United States is:

1. A seal structure of the class described comprising a vitreous core, a lead-in conductor comprising a plurality of spaced thin strips of metal extending along said core and terminating in a cross piece portion over one end of said core, a rod-like metal member in alignment with said core and having one end united to said cross piece portion of the conductor, and a vitreous Jacket surrounding said core and rod-like memleer, said strips being fused between the adiacent portions oi said core and Jacket. 

